1. Field of the Invention
The present invention relates to a printing apparatus, and more particularly to an impact printing apparatus provided with a mechanism for erasing or correcting printed characters through an erasing ribbon.
2. Description of the Prior Art
In a conventional typewriter or the like, the erasure of a printed character is achieved by moving the printing head to the character to be erased and striking the same character through an erasing ribbon. The erasing ribbon may be composed of an adhesive tape for lifting off the printed ink from the printing sheet, or of a tape coated with a material of a color the same as that of the printing sheet for covering the character to be erased.
In such conventional printing apparatus with a so-called overlap typing mechanism for erasure, incomplete erasure has often been observed because the carriage moving mechanism is not precise enough for printing the same character again exactly on the previously printed character and can only stop the carriage in a slightly different position. Such an incompletely erased character smears a character newly printed thereon, thus providing an extremely undesirable finish.
Such overlap typing correction, if to be made complete through improved precision of the mechanism, will lead to a significantly higher manufacturing cost. Also U.S. Pat. No. 4,307,971 discloses a mechanism for achieving such overlap typing through a slight movement of the carriage, but a precise function is difficult to achieve in practice in consideration of the large weight of the carriage.